1. Field Of The Invention
The present invention pertains to exhaust mufflers for watercraft, and more particularly to a method and apparatus for preventing or minimizing explosion damage by wet marine exhaust mufflers. A preferred embodiment of the invention comprises a muffler having a metallic housing encapsulated in a polymeric jacket to promote the integrity of the muffler when subjected to high internal pressure surges.
2. Description Of The Related Art
Motorized watercraft typically have included exhaust mufflers for muffling or attenuating exhaust noise generated by the operation of marine engines. Such mufflers have had to be capable of handling not only exhaust gas itself, but also droplets of water injected into the exhaust flow from the cooling system of the engine. The water injected from the engine cooling system typically performed two functions, namely, absorbing engine exhaust noise and cooling the exhaust gas so that the gas might be safely discharged through the hull of the craft without presenting a fire hazard.
Mufflers of various designs have been placed in the exhaust conduits running between the engines and the discharges. Typically, marine mufflers include housings which enclose one or more chambers for permitting expansion of the exhaust gas to attenuate noise. One example of a wet marine exhaust muffler is disclosed in U.S. Pat. No. 5,588,888 to Magharious, the disclosure of which is incorporated herein by reference. Often, marine muffler designs have been closely akin to the mufflers used on automobiles but have been constructed of fiber reinforced polymer materials such as FIBERGLASS materials which can better tolerate the marine environment.
Drawbacks to the use of fiber reinforced polymer materials as opposed to metals in the fabrication of exhaust mufflers have included lower strength and greater elasticity in comparison to metals. For example, acoustical energy in the exhaust gas passing through the muffler could induce sympathetic elastic vibrations in the walls of the housing. Such vibrations reduce the ability of the muffler to attenuate acoustical noise and may also contribute to possible failure of the housing walls.
Under certain circumstances, wet marine exhaust mufflers have been exposed to abnormally high internal pressure surges (that is, "backfires") sufficient to cause the mufflers to explode. Such explosions are capable of causing damage to the craft in which the mufflers were installed as well as injury to persons positioned in or near the craft.
Past efforts to prevent or reduce explosion damage have included changes in the configurations (e.g., geometries, chamber sizes, pipe positions and the like) of the mufflers and in the materials from which the mufflers were made. Such changes significantly increase the costs of manufacturing the mufflers. The changes also require compromises in other desirable characteristics of the mufflers, such as corrosion resistance and accoustical characteristics.
Consequently, there remains a need for a wet marine exhaust muffler, and for a method for manufacturing such a muffler, effective to prevent or minimize explosion damage without substantially increasing the manufacturing cost or compromising other desirable muffler characteristics.